Pruebas en ls servicios con señales

calculator.service.ts

  it('should be created', () => {
    // todo:
  });

  it('should be created with default values', () => {
    // todo:
  });

  it('should set resultText, subResultText to "0" when C is pressed', () => {
    // todo:
  });

  it('should update resultText with number input', () => {
    // todo:
  });

  it('should handle operators correctly', () => {
    // todo:
  });

  it('should calculate result correctly for addition', () => {
    // todo:
  });

  it('should calculate result correctly for subtraction', () => {
    // todo:
  });

  it('should calculate result correctly for multiplication', () => {
    // todo:
  });

  it('should calculate result correctly for division', () => {
    // todo:
  });

  it('should handle decimal point correctly', () => {
    // todo:
  });

  it('should handle decimal point starting with 0', () => {
    // todo:
  });

  it('should handle sign change +/-', () => {
    // todo:
  });

  it('should handle backspace', () => {
    // todo:
  });

  it('should handle backspace with negative numbers', () => {
    // todo:
  });

  it('should handle max length', () => {
    // todo:
  });

  it('should handle invalid input', () => {
    // todo:
  });

  it('should handle negative zero input correctly', () => {
    // todo:
  });